Process of and apparatus for the manufacture of sulphate of lead



May 27, 1924 J. GITSHAM ET A].

PROCESS OF AND APPARATUS FOR THE MANUFACTURE OF SULPHATE OF LEAD Filed May 8, 1922 v V P l b hlflnhl l p l I I I I I l I Patented May 27, 192 2.

JAMES GITSHAIVI AND HAROLD ROBERT EVERSHED, 0F L-AUNCESTON, TASMANIA, AUSTRALIA.

PROCESS OF AND APPARATUS FO'B THE Application filed May 8,

To all whom it may concern:

Be it known that we, JAMES Grrsrmrrand Hauonn ROBERT EVERSHED, both subjects of the King of Great Britain, residing at 175 George Street, Launceston, in the State of Tasmania, Australia, have invented certain new Processes of and Apparatus for the Manufacture of Sulphate of Lead, of which the following is a specification.

This invention has for its object the manufacture of sulphate of lead from the sulphide, as it occurs in the ore, to fulfill the conditions of a pigment laid down by the British Departmental Report on the Use of paints containing lead in the paintingrof buildings,'dated November, 191

A process of this kind has been described in which sulphate, sulphide and oxide of lead are obtained directly from the raw sulphide by introducing the same in a finely divided state into an electric furnace wherein the fine sulphides are volatilized and afterwards rendered into sulphates by the action of oxygen. The product is then separated and recovered for use.

In the process above indicated some sulphite and oxide of lead is produced with the sulphate: this is to be avoided or minimized as much as possible owing to the fact that the oxide and sulphite are not only deleterious when present in any considerable proportions but detract from the appearance of the sulphate when associated therewith. It has also been found that the draft of air through the furnace carries with it not only the fumed sulphides but a certain pe rceutage of unfumed material that has come within the influence of the draft and has been prevented from reaching the arcs of the furnace.

Our present invention aims at the production of a purer sulphate of lead and the elimination of the said unfumed sulphide. According to the invention we take a sulphide of lead ore, not necessarily pure, and very finely subdivide the same before passing it in nicely regulated quantities in a suitable feeding appliance to the arcs of an electric furnace. The electrodes are arranged horizontally in the furnace in two or more pairs and as the material falls there on it is immediately turned into fume by the extremely high temperature emanating from the electrodes. In, the side of the fur- .ace some feet above the arcs is an air con- MANUFACTURE OF SULPI-IATE 0F LEAD.

1922. Serial No. 559,370.

duit through which a supply from the atmosphere is constantly drawn and which, after passing over the furnace, flows through flues carrying with it the fumed material. The suspended hot and minute sulphide fume is converted into sulphate of lead by contact with the atmosphericoxygen and is furthermore met in the lines by a series of line water sprays which continuously operate all along the flue and wash down the material which is then conducted as a sulphate of lead to suitable settling vats. Associated with the water sprays we may also use steam jets with good effect and the spraying is continued along the fines until all the fume is brought down.

In the vats means are provided for warm ing and agitating the product, such as by coils delivering steam thereinto, and while the agitation is in progress free acid may be added to the vat in sufficient strength to convert remaining sulphites and oxides into sulphates. The agitation will have the efiect of floating any raw sulphide that may have escaped the fuming process and this is skimmed ofi', dried, and afterwards retreated. The remainder will then be subjected to treatn'ient with lime water in sufficient quantities to neutralize the acid, and the sulphates, after settling, will be decanted from the vats, dried and packed for use as a lead pigment.

If the sulphide ore is not pure it should, after the ordinary crushing, be suitably conccntratedto remove the gangue before fuming, and a pure sulphide, as nearly as economically possible, obtained before passing it to the arcs. We preferably use three arcs in our furnace with a three phase alternating current transformed to a low voltage and high amperage controlled by metallic choking coils. The sulphide fume will be con- Verted to sulphate largely by contact with the atmospheric oxygen and the acid manufactured in the fines, but a percentage of the sulphide will be converted only to sulphite and oxide. The acid formed in the flues through the chemical combination of the sulphur with the water and steam will effect the conversion of much of the sulphides and also some of the sulphites and oxides into sulphates, but should an appreciable quantity of non-sulphates remain, say in excess of five per cent, then the free acid should be added in the vats.

It will be possible to select an ore having a sulphur content sufficient to provide in the flues for an excess of acid to affect all or nearly all the sulphites and oxides and to render unnecessary the addition of free acid in the vats. It will also be possible to so select the materials that only enough sulphur will be involved to provide acid to combine with the unconverted sulphides, sulphites and oxides to obtain a product in the vats free of an excess of acid, thereby rendering unnecessary the lime treatment. Should, however, inconvenient quantities of sulphite and oxide be found in the vats the added acid will be employed to convert the same into sulphates and the acid will afterwarus be neutralized by the lime, the result ing precipitate of calcium sulphate remaining with. the lead sulphate.

it convenient apparatus wherein our process can be carried into effect is shown on the accompanying drawings, in which Figure 1 is a diagrammatic plan of the furnace, fines and vats, and

Figure 2 is a sectional elevation of the furnace.

In the furnace, the electrodes 1, 2 and 3 are arranged in pairs about nine (9) inches above the floor and about five feet. above the arcs is an atmospheric air intake l of ample proportions, through which air is drawn by the fans 5. Opposite said intake is an outlet for the air which will convey the fume in the furnace to a bifurcated flue 6, down which the air and fume pass under the water sprays 7, the steam jets not being shown in the drawing. The draft in the lines will. be assisted by the uptake or chimney 8.

As the material is washed down in the flues it will fiow with the water into the launders and from thence into the vats 10. Fitted to the vats is a steam pipe 11 that runs the length of the system and is eon nccted up to each vat wherein is a perforated steam pipe upon the floor thereof that delivers steam upwardly into the mixture to warm and agitate the same. The other pipe 12 is intended to supply a weak solution of lime water to the vats, when required, the pipe leading from a suitable tank and is fitted with the usual. cocks, not shown in the drawing.

The finely divided material is fed through an opening in the furnace wall on to the arcs in regulated quantities and is turned at once into fume which rises into the current of air passing through the top of the furnace taking up oxygen therefrom on its way to the lines. In the fines more sulphates are formed and washed out into the vats. After agitation in the vats the material will yield up some unfuined lead sulphide by flotation and this will be removed for retreatment. Then free acid is added, when necessary, to convert to sulphates the sulphites and oxides of lead, and any excess of acid is neutralized by the weak solution of lime water, which precipitates as calcium sulphate and can mingle with the sulphate of lead without serious detriment thereto.

Having now described our invention what we claim as new and desire to secure by Letters Patent is 1. The process of making lead sulphate which consists in feeding finely divided lead sulphide over and on to the arcs of an electrie furnace to fume the ore, withdrawing the fume in a lateral draft of atmospheric air from the furnace into flues, subjecting the material therein to fine water sprays to recover lead sulphate in vats and heating and agitating the mixture in the vats to recover any unfumed sulphide.

2. The process of making lead sulphate which consists in feeding same on to the arcs of an electric furnace to fume the ore, withdrawing the fume in a lateral draft of atmospheric air from the furnace into fiues, subjecting the material therein to fine water sprays that wash it into vats mainly as lead sulphate and heating and agitating the mixture in the vats to recover unfumed sulphide, and wherein steam jets are used with the water jets to mingle with the fume in the fines and free acid is added to the vats to turn unconverted sulphites and oxides of lead into sulphates said acid condition being afterwards neutralized by a weak solution of lime water before decanting the sulphates.

3. In the i'i'ianufacture of lead sulphate. the treatment of lead sulphide ore in a very finely divided condition by feeding same on to the arcs of an electric furnace to fume the ore and withdrawing the fume with atmospheric air into a fine wherein it is subjected to water sprays to form an acid that assists to convert the material into sulphates.

In testimony whereof we affix our signatures.

JAMES GITSHAM. HAROLD ROBERT EVERSHED. 

